NAME
upx - compress or expand executable files
SYNOPSIS
upx [ *command* ] [ *options* ] *filename*...
ABSTRACT
The Ultimate Packer for eXecutables
Copyright (c) 1996-2000 Markus Oberhumer & Laszlo Molnar
http://wildsau.idv.uni-linz.ac.at/mfx/upx.html
http://www.nexus.hu/upx
http://upx.tsx.org
UPX is a portable, extendable, high-performance executable
packer for several different executable formats. It achieves an
excellent compression ratio and offers **very** fast
decompression. Your executables suffer no memory overhead or
other drawbacks for most of the formats supported.
While you may use UPX freely for both non-commercial and
commercial executables (for details see the file LICENSE), we
would highly appreciate if you credit UPX and ourselves in the
documentation, possibly including a reference to the UPX home
page. Thanks.
[ Using UPX in non-OpenSource applications without proper
credits is considered not politically correct ;-) ]
DISCLAIMER
UPX comes with ABSOLUTELY NO WARRANTY; for details see the file
LICENSE.
Having said that, we think that UPX is quite stable now. Indeed
we have compressed lots of files without any problems. Also, the
current version has undergone several months of beta testing -
actually it\'s almost 2 years since our first public beta.
This is the first production quality release, and we plan that
future 1.xx releases will be backward compatible with this
version.
Please report all problems or suggestions to the authors.
Thanks.
DESCRIPTION
UPX is a versatile executable packer with the following
features:
- excellent compression ratio: compresses better than zip/gzip,
use UPX to decrease the size of your distribution !
- very fast decompression: about 10 MB/sec even on my old Pentium 133
- no memory overhead for your compressed executables for most of the
supported formats
- safe: you can list, test and unpack your executables
Also, a checksum of both the compressed and uncompressed file is
maintained internally.
- universal: UPX can pack a number of executable formats:
* dos/exe
* dos/sys
* dos/com
* djgpp2/coff
* watcom/le (supporting DOS4G, PMODE/W, DOS32a and CauseWay)
* win32/pe
* rtm32/pe
* tmt/adam
* linux/i386
* atari/tos
- portable: UPX is written in portable endian-neutral C++
- extendable: because of the class layout it\'s very easy to support
new executable formats or add new compression algorithms
- free: UPX can be distributed and used freely. And from version 0.99
the full source code of UPX is released under the GNU General Public
License (GPL) !
You probably understand now why we call UPX the \"*ultimate*\"
executable packer.
COMMANDS
Compress
This is the default operation, eg. upx yourfile will compress
the file specified on the command line.
Decompress
All UPX supported file formats can be unpacked using the -d
switch, eg. upx -d yourfile will uncompress the file you\'ve just
compressed.
Test
The -t command tests the integrity of the compressed and
uncompressed data, eg. upx -t yourfile check whether your file
can be safely decompressed. Note, that this command doesn\'t
check the whole file, only the part that will be uncompressed
during program execution. This means that you should not use
this command instead of a virus checker.
List
The -l command prints out some information about the compressed
files specified on the command line as parameters, eg upx -l
yourfile shows the compressed / uncompressed size and the
compression ratio of *yourfile*.
OPTIONS
-q: be quiet, suppress warnings
-q -q (or -qq): be very quiet, suppress errors
-q -q -q (or -qqq): produce no output at all
--help: prints the help
--version: printf the version of upx
--stdout: writes all output to stdout
??? Markus, should we specify here all the options ???
COMPRESSION LEVELS & TUNING
UPX offers ten different compression levels from -1 to -9, and -
-best. The default compression level is -7.
* Compression levels 1, 2 and 3 are pretty fast.
* Compression levels 4, 5 and 6 achieve a good time/ratio
performance.
* Compression levels 7, 8 and 9 favor compression ratio over
speed.
* Compression level --best may take a very long time.
Note that compression level -9 can be quite slow for some large
files, but you definitely should use it when releasing a final
version of your program. (E.g. it took about 20 minutes to
compress the almost 5 MB MAME 0.34 with -9 on my Pentium 133,
but the resulting executable was still ~65 kB smaller than when
using -7.)
Since UPX 0.70 there is also an extra compression level --best
which squeezes out even some more compression ratio. While it is
usually fine to use this option with your favorite .com file it
may take several hours to compress a multi-megabyte program. You
have been warned.
Tips for even better compression:
* Try if --overlay=strip works.
* For win32/pe programs there\'s --strip-relocs=0. See notes below.
OVERLAY HANDLING OPTIONS
UPX handles overlays like many other executable packers do: it
simply copies the overlay after the compressed image. This works
with some files, but doesn\'t work with others.
Since version 0.90 UPX defaults to --overlay=copy for all
executable formats.
--overlay=copy Copy any extra data attached to the file. [DEFAULT]
--overlay=strip Strip any overlay from the program instead of
copying it. Be warned, this may make the compressed
program crash or otherwise unusable.
--overlay=skip Refuse to compress any program which has an overlay.
ENVIRONMENT
The environment variable UPX can hold a set of default options
for UPX. These options are interpreted first and can be
overwritten by explicit command line parameters. For example:
for DOS/Windows: set UPX=-9 --compress-icons#1
for sh/ksh/zsh: UPX=\"-9 --compress-icons=1\"; export UPX
for csh/tcsh: setenv UPX \"-9 --compress-icons=1\"
Under DOS/Windows you must use \'#\' instead of \'=\' when setting
the environment variable because of a command.com limitiation.
On Vax/VMS, the name of the environment variable is UPX_OPT, to
avoid a conflict with the symbol set for invocation of the
program.
Not all of the options are valid in the environment variable -
UPX will tell you.
You can use the --no-env option to turn this support off.
NOTES FOR THE SUPPORTED EXECUTABLE FORMATS
NOTES FOR ATARI/TOS
This is the executable format used by the Atari ST, a 68000
based personal computer which was popular in the late \'80s.
Support of this format is only because of nostalgic feelings of
one of the authors and serves no practical purpose :-).
Packed programs will be byte-identical to the original after
uncompression. All debug information will be stripped, though.
Extra options available for this executable format:
(none)
NOTES FOR DOS/COM
Obviously UPX won\'t work with executables that want to read data
from themselves (like some commandline utilities that ship with
Win95/98).
Compressed programs only work on a 286+.
Packed programs will be byte-identical to the original after
uncompression.
Maximum uncompressed size: ~65100 bytes.
Extra options available for this executable format:
--8086 Create an executable that works on any 8086 CPU.
NOTES FOR DOS/EXE
dos/exe stands for all \"normal\" 16-bit DOS executables.
Obviously UPX won\'t work with executables that want to read data
from themselves (like some command line utilities that ship with
Win95/98).
Compressed programs only work on a 286+.
Extra options available for this executable format:
--8086 Create an executable that works on any 8086 CPU.
--no-reloc Use no relocation records in the exe header.
NOTES FOR DOS/SYS
You can only compress plain sys files, sys/exe (two in one)
combos are not supported.
Compressed programs only work on a 286+.
Packed programs will be byte-identical to the original after
uncompression.
Maximum uncompressed size: ~65350 bytes.
Extra options available for this executable format:
--8086 Create an executable that works on any 8086 CPU.
NOTES FOR DJGPP2/COFF
First of all, it is recommended to use UPX *instead* of strip.
strip has the very bad habit of replacing your stub with its own
(outdated) version. Additionally UPX corrects a bug/feature in
strip v2.8.x: it will fix the 4 KByte aligment of the stub.
UPX includes the full functionality of stubify. This means it
will automatically stubify your COFF files. Use the option --
coff to disable this behaviour (see below).
UPX automatically handles Allegro packfiles.
The DLM format (a rather exotic shared library extension) is not
supported.
Packed programs will be byte-identical to the original after
uncompression. All debug information and trailing garbage will
be stripped, though.
BTW, UPX is the successor of the DJP executable packer.
Extra options available for this executable format:
--coff Produce COFF output instead of EXE. By default
UPX keeps your current stub.
NOTES FOR LINUX/i386
How it works:
Because Linux is a real operating system, the in-place in-memory
decompression scheme used in the other executable formats doesn\'t
work here.
Instead we must use temporary decompression to disk. Interestingly -
because of the good memory management of the Linux kernel - this
often does not introduce a noticable delay, and in fact there
will be no disk access at all if you have enough free memory as
the entire process takes places within the filesystem buffers.
A compressed executable consists of the UPX stub and an overlay
which contains the original program in a compressed form.
The UPX stub is a statically linked ELF executable and does
the following at program startup:
1) decompress the overlay to a temporary location in /tmp
2) open the temporary file for reading
3) try to delete the temporary file and start (execve)
the uncompressed program in /tmp using /proc/self/fd/X as
attained by step 2)
4) if that fails, fork off a subprocess to clean up and
start the program in /tmp in the meantime
The UPX stub is about 1700 bytes long, partly written in assembler
and only uses kernel syscalls. It is not linked against any libc.
Benefits:
- UPX can compress all executables, be it AOUT, ELF, libc4, libc5,
libc6, Shell/Perl/Python/... scripts, standalone Java .class
binaries, or whatever...
All scripts and programs will work just as before.
- Compressed programs are completely self-contained. No need for
any external program.
- UPX keeps your original program untouched. This means that
after decompression you will have a byte-identical version,
and you can use UPX as a file compressor just like gzip.
[ Note that UPX maintains a checksum of the file internally,
so it is indeed a reliable alternative. ]
- As the stub only uses syscalls and isn\'t linked against libc it
should run under any Linux configuration that can run ELF
binaries and has working /proc support.
- For the same reason compressed executables should run under
FreeBSD and other systems which can run Linux binaries.
[ Please send feedback on this topic ]
Drawbacks:
- You need additional free disk space for the uncompressed program
in your /tmp directory. This program is deleted immediately after
decompression, but you still need it for the full execution time
of the program.
- You must have /proc filesystem support as the stub wants to open
/proc/self/exe and needs /proc/self/fd/X. This also means that you
cannot compress programs that are used during the boot sequence
before /proc is mounted.
- `ldd\' and `size\' won\'t show anything useful because all they
see is the statically linked stub (as of 0.82 the section headers
are stripped from the UPX stub and `size\' doesn\'t even recognize
the file format any longer - looks like a binutils bug).
- Utilities like `top\' will display numerical values in the process
name field. This is because Linux computes the process name from
the first argument of the last execve syscall (which is typically
something like /proc/self/fd/3).
- To reduce memory requirements during uncompression UPX splits the
original file into blocks, so the compression ratio is a little bit
worse than with the other executable formats (but still quite nice).
[ Advise from kernel experts which can tell me more about the
execve memory semantics is welcome. Maybe this shortcoming
could be removed. ]
- Because of temporary decompression to disk the decompression speed
is not as fast as with the other executable formats. Still, I can see
no noticable delay when starting programs like my ~3 MB emacs (which
is less than 1 MB when compressed :-).
Notes:
- As UPX leaves your original program untouched it is advantageous
to strip it before compression.
- It is not advisable to compress programs which usually have many
instances running (like `make\') because the common segments of
compressed programs won\'t be shared any longer between different
processes.
- If you compress a script you will lose platform independence -
this could be a problem if you are using NFS mounted disks.
- Compression of suid, guid and sticky-bit programs is rejected
because of possible security implications.
- For the same reason there is no sense in making any compressed
program suid. You wouldn\'t trust sourcecodeless anyway, would
you ? ;-)
- Obviously UPX won\'t work with executables that want to read data
from themselves. E.g., this might be a problem for Perl scripts
which access their __DATA__ lines.
- In case of internal errors the stub will abort with exitcode 127.
Typical reasons for this to happen are that the program has somehow
been modified after compression, you have run out of disk space
or your /proc filesystem is not yet mounted.
Running `strace -o strace.log compressed_exe\' will tell you more.
Extra options available for this executable format:
(none)
NOTES FOR RTM32/PE
Same as win32/pe.
NOTES FOR TMT/ADAM
This format is used by the TMT Pascal compiler - see
http://www.tmt.com/ .
Extra options available for this executable format:
(none)
NOTES FOR WATCOM/LE
UPX has been successfully tested with the following extenders:
DOS4G, DOS4GW, PMODE/W, DOS32a, CauseWay. The WDOS/X extender is
partly supported (for details see the file bugs BUGS).
Yes, you can use your compressed executables with DOS4GW.
The LX format is not yet supported.
DLLs are not supported.
Extra options available for this executable format:
--le Produce an unbound LE output instead of
keeping the current stub.
NOTES FOR WIN32/PE
The PE support in UPX is quite stable now, but definitely there
are still some incompabilities with some files.
Because of the way upx (and other packers for this format)
works, you can see increased memory usage of your compressed
files. If you start several instances of huge compressed
programs, you\'re wasting memory. On the other hand if you\'re
compressing only smaller programs, or running only one instance
of larger programs, then this penalty is smaller, but it\'s still
there.
If you\'re running executables from network, then compressed
programs will load faster, and require less bandwidth during
execution.
DLLs are supported.
Extra options available for this executable format:
--compress-exports=0 Don\'t compress the export section.
Use this if you plan to run the compressed
program under Wine.
--compress-exports=1 Compress the export section. [DEFAULT]
Compression of the export section can improve the
compression ratio quite a bit but may not work
with all programs (like winword.exe).
UPX never compresses the export section of a DLL
regardless of this option.
--compress-icons=0 Don\'t compress any icons.
--compress-icons=1 Compress all but the first icon.
--compress-icons=2 Compress all icons which are not in the
first icon directory. [DEFAULT]
--compress-resources=0 Don\'t compress any resources at all.
--force Force compression even when there is an
unexpected value in a header field.
Use with care.
--strip-relocs=0 Don\'t strip relocation records.
--strip-relocs=1 Strip relocation records. [DEFAULT]
This option only works on executables with base
address greater or equal to 0x400000. Usually the
compressed files becomes smaller, but some files
may become larger. Note that the resulting file will
not work under Win32s.
DIAGNOSTICS
Exit status is normally 0; if an error occurs, exit status is 1.
If a warning occurs, exit status is 2.
UPX\'s diagnostics are intended to be self-explanatory.
BUGS
Please report all bugs immediately to the authors.
AUTHORS
Markus F.X.J. Oberhumer
http://wildsau.idv.uni-linz.ac.at/mfx/upx.html
Laszlo Molnar
http://www.nexus.hu/upx
COPYRIGHT
Copyright (C) 1996-2000 Markus Franz Xaver Johannes Oberhumer
Copyright (C) 1996-2000 Laszlo Molnar
This program may be used freely, and you are welcome to
redistribute it under certain conditions.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the UPX
License Agreement for more details.
You should have received a copy of the UPX License Agreement
along with this program; see the file LICENSE. If not, visit the
UPX home page.
